One type of process cartridge employed in an image-forming device disclosed in U.S. Pat. No. 6,330,410 includes a drum cartridge accommodating a photosensitive drum, and a developer cartridge (toner cartridge) that is detachably mounted on the drum cartridge. The developer cartridge is provided with a developing roller for carrying toner on the surface thereof in order to develop electrostatic latent images formed on the photosensitive drum.